1. Field of the Invention
This invention pertains to a compact device for holding and accurately aligning a mask used in the fabrication of integrated circuits and components on semiconductor wafer substrates. Multiple masks are employed in the semiconductor fabrication process and each must be aligned in spatial relation with the wafer on which the fabrication operations are to be performed in sequential steps. Sub-micron alignment tolerances are often required. In practice, the mask must be held and initially accurately positioned and a wafer is then moved or positioned at a series of predetermined positions so as to perform, for example, various photo-lithography steps by X-ray, ultraviolet or other electron or photon means on the wafer substrate.
2. Description of the Prior Art
The functions of masks in wafer fabrication processes are described in U.S. Pat. Nos. 4,037,969 and 4,326,805 where an X-ray lithographic system is disclosed particularly involving the relative alignment of mask-to-wafer including mask-to-wafer separation.
U.S. Pat. No. 4,185,202 (FIG. 4) shows a typical mask holding device in which the mask is spring mounted between a series of lower pin members and an upper overhanging element fixed to the main frame for holding the wafer and mask. Such a mask holder does not allow for accurate orientation or alignment of the mask nor does it rigidly hold the mask in fixed position relative to the wafer. The mask can be easily rotated, moved laterally, or canted and is dependent on the spring forces of the individual springs and accurate sizing of the pin elements.